Various techniques are known for monitoring transmissions from signal sources such as a television station, a radio station, satellite and cable television providers (referred to collectively hereinafter as “broadcast source”). The signal of interest might be a program being transmitted by cable or satellite, or it might be a recorded program being played back on a DVD or VCR. The program may be a “show” providing musical or dramatic entertainment, or it might be a commercial. The monitoring is carried out to provide information that, for example, reveals the size of the audience tuned to a given broadcast source at a given time of day, determines the total number of people who have seen a program, provides independent validation that a commercial has been broadcast, and so on. Such information is useful for broadcasters, advertisers, etc. As used hereinafter, the term “program signal” is intended to include all such signals, be they, for example, a real time broadcast or one that has been recorded, to be suitably reproduced to be electronically performed for viewing by an audience of a show or a commercial about which such information is being collected.
One approach that has been adopted to perform such monitoring is to combine the audio portion of a program signal with a code signal. This is disclosed in U.S. Pat. No. 4,718,106. Other approaches utilizing such a combined signal are disclosed in U.S. Pat. Nos. 5,457,807 and 5,630,203. The combined signal is made available, such as by on-air broadcast, to an intended audience. The audio signal, including the code portion, is reproduced by the speaker. Certain members of the intended audience who agree to participate in such monitoring are provided with a portable monitoring apparatus that is to be worn by these members and which can detect the code portion of the combined signal as reproduced by the speaker.
When a television set, for example, is placed in what is conventionally known as a mute mode, the audio portion of the program signal is inhibited from producing sound by blocking it from reaching the speaker. Of course, since the code portion is part of the audio signal, muting also results in suppressing the code signal from being reproduced by the speaker. In the absence of such a reproduced code signal, it is not possible to continue monitoring the program signal by relying on the code portion of the combined signal. Consequently, a mute mode creates a gap in the capability of the monitoring apparatus to perform the desired monitoring tasks.
Continuing to perform monitoring tasks even during muting is useful because the viewer can still be watching the program and/or the commercials even though the audio is muted. In fact, for some situations the sound can be inaudible in the normal mode of viewing the program, such as for deaf persons, or in a very noisy environment such as a bar. For such instances, there may be closed captioned text displayed on the TV screen corresponding to the audio portion of the program. Also, when commercial validation is being performed (i.e., to check whether a commercial that has been paid for is actually transmitted by the broadcast source), the commercial might coincidentally be shown during muting. In such a case, the monitoring results would be incorrect because they would indicate that the commercial was not broadcast when, it fact, it was. In such a situation, obtaining monitoring information during muting would be of critical importance to determine whether or not a commercial which has been paid for has actually been broadcast. Thus, it is highly desirable to maintain the monitoring capability even though a mute mode has been actuated.
U.S. Pat. No. 5,574,963 provides a solution which involves a switch that feeds only the code portion of the audio signal to the speaker even while the rest of the audio signal is blocked from reaching the speaker. Although this approach is effective to enable monitoring to continue even during a mute mode, it has the shortcoming of requiring a retrofit of the TV set by wiring a special switch into its circuitry. It is preferable to avoid such a task in order to eliminate an inconvenience to the household where the monitoring is to take place, and also the attendant costs to the monitoring service provider.